In Angle of Arrival (AoA) or any location technology used to locate wireless device, it is desirable to reduce location error due to signal-to-noise ratio (SNR) and multipath in order to achieve more accurate location results. In AoA-based location techniques, raw data (from channel state information or raw in-phase/quadrature-phase samples) is converted into phase vectors that are supplied as input to the AoA-based location solution. The manner in which the phase vectors are converted and ultimately input into the AoA-based computation can significantly affect accuracy.
Phase estimates at the antennas of a circular or other geometric antenna array are used to estimate the incident direction of radio waves. In 802.11, it is convenient to use the channel estimate from packet reception in estimating this phase. However, using the channel estimate limits scalability since there is only 1 or 2 long training fields (LTFs) per PPDU. Therefore, in order to capture AoA estimates in a system with a switched antenna array, multiple PPDUs need to be sent to capture every antenna state. In order to decrease the number of PPDUs required, switching can occur during the PPDU, but the LTF cannot be the lone source of the channel estimate.
IEEE 802.11ax introduces Orthogonal Frequency Division Multiple Access (OFDMA), where client traffic no longer occupies the entire signal bandwidth. Instead, clients are allocated resource units (RUs) or subsets of the full signal spectrum and transmit or receive at the same time. OFDMA provides a way to vastly increase the scalability of AoA location by capturing the AoA estimate for many clients at the same time. However, obtaining the channel estimate on a per client basis while switching through the states of an antenna array presents challenges.